The present invention relates to a stent-graft for use as a prosthetic within a body lumen to support the lumen, and particularly, to a stent-graft having improved longitudinal structural flexibility and graft wear that can be used within a body to support a lumen.
It is generally known to insert a resiliently expandable stent into a body lumen, such as a blood vessel, to provide radial hoop support within the lumen in the treatment of atherosclerotic stenosis and other conditions. For example, it is generally known to open a blocked cardiac blood vessel by conventional methods (e.g., balloon angioplasty or laser ablation) and to keep that blood vessel open using an expandable stent.
Stents are tubular structures formed of biocompatible materials, usually metals like stainless steel or Nitinol, which are radially expandable. The radial strength of the stent material keeps the stent and the lumen into which the stent is deployed in an open configuration. Expandable stents typically include a mesh-like surface pattern of slots or holes cut therein so that a balloon can expand the stent after the stent has been deployed into the body lumen and positioned at a predetermined location. However, these mesh-like surface patterns also permit the passage of endothelial and other cells through the openings in the stents that can cause restenosis of the vessels. For example, the mesh-like surface patterns can permit thrombus formations and plaque buildup within the vessel.
Expandable stents have been combined with coverings of biocompatible materials to form xe2x80x9cstent-graftsxe2x80x9d that provide benefits in addition to those provided by conventional expandable stents. For example, the expandable stent-grafts can be used as a graft within a body lumen, such as a blood vessel. Intraluminal vascular stent-grafts can be used to repair aneurysmal vessels, particularly aortic arteries, by inserting an intraluminal vascular stent-graft within the aneurysmal vessel so that the prosthetic stent-graft support the vessel and withstand the forces within the vessel that are responsible for creating the aneurysm.
Polytetrafluroethylene (PTFE) has been used as a material from which to fabricate blood vessel grafts or prostheses used to replace damaged or diseased vessels.
This is partially because PTFE is extremely biocompatible causing little or no immunogenic reaction when placed within the human body. Additionally, in a preferred form, expanded PTFE (ePTFE) has been used. This material is light and porous and is potentially colonized by living cells becoming a permanent part of the body. The process of making ePTFE of vascular graft grade is well known.
Enclosing a stent with ePTFE can create a vascular prosthetic that limits the amount of cellular material that can enter the stent and the blood vessel. However, such a stent-graft tends to be rather inflexible. Conventional stent-grafts tend not to conform to the natural curved shape of the blood vessel in which they are deployed. In particular, conventional stent-grafts can be longitudinally inflexible (i.e., along a length of the stent portion and the graft portion), and therefore tend to be resistant to transverse deformation. As a result, these stent-grafts may not effectively seal the intended aneurysm(s) within the blood vessel in which the stent-graft is deployed.
Conventional stent-grafts include circumferential support members (hoops) that are securely spaced from each other and from the ends of the stent portion so that they do not experience relative axial movement. The spacing between adjacent support elements is maintained by rigid connections or bridge elements (sometimes referred to in the art as xe2x80x9cbridgesxe2x80x9d) between adjacent support elements and at least one elongated member that extends from a first end of the stent portion to a second end of the stent portion. The circumferential support members are also secured to the graft portion of material extending along the stent portion so that the graft portion cannot move along the length of the stent portion. These secure, rigid connections prevent the support elements and the graft portion from moving longitudinally along the elongated member(s) of the stent and prevent the stent-graft from conforming to the curvature of the blood vessel in which it is deployed. The interaction of the conventional stent material and the conventional graft material, along with the large expanded diameter of a stent-graft, create conformability, performance and manufacturing issues that are in addition to those issues associated with conventional stents and discussed in copending U.S. patent application Ser. No. 10/100,986 which is hereby incorporated by reference. For example, poor longitudinal flexibility of the stent-graft can lead to kinking of the graft portion and the ultimate occlusion of the flow lumen. Additional disadvantageous of conventional stent-grafts can include graft wear on the stent portion, blood leakage through suture holes in the graft portion that receive the sutures that anchor the graft portion to the stent portion and labor intensive manufacturing processes.
There is a need in the art for a stent-graft that is longitudinally flexible, while providing a smooth inner surface for blood flow.
The present invention relates to a stent-graft with increased longitudinal flexibility relative to conventional stent-grafts. Longitudinal flexibility as used herein relates to the flexibility of the stent-graft structure (or portions thereof) to move relative to its major, longitudinal axis of extension. The stent-graft is deployed within a body lumen for supporting the lumen and repairing luminal aneurysms. In a preferred embodiment, the stent-graft is located and expanded within a blood vessel to repair aortic aneurysms.
In an embodiment, the stent-graft can be comprised of an expandable stent portion, an expandable graft portion and at least one elongated rail. The stent portion and graft portion are moveable between the terminal ends of the rail(s) and relative to the rails so that the stent-graft can conform to the shape of a vessel in which it is deployed. Additionally, longitudinally adjacent circumferential support elements of the stent portion can be secured together by at least one bridging element. Alternatively, each circumferential support elements can be free of a connection to a longitudinally adjacent circumferential support element. The use of the rail(s) and the bridging elements allows the support elements to separate as needed, assume the outer radius of a vessel bend and shorten to assume an inner radius of a vessel bend. The stent-graft eliminates the poor longitudinal flexibility associated with conventional stent-grafts. As a result, the stent-graft of the present invention provides greater resistance to kinking after expansion, and thus, eliminates the potential for the graft portion occluding the blood flow lumen. Moreover, the wear on the graft is reduced and its longevity increased.
Furthermore, according to an aspect of the present invention, the graft portion of the stent-graft is coupled to at least one longitudinal extending rail at locations spaced from the ends of the stent-graft. In one embodiment, the graft portion is coupled to the rails at the locations spaced from the ends of the stent-graft without the use of sutures that would extend through the graft portion and compromise the fluid retention integrity of the graft portion at these spaced locations. Instead, circumferential coupling members positioned about the graft portion and secured to the graft portion can receive the rails. These coupling members include circumferentially spaced openings that receive the rail(s). Alternatively, the rails extend through cauterized holes that were mechanically created in a substrate of the graft portion. Passing the rail(s) through these openings and holes reduces manufacturing costs and time. Passing the rail(s) also provides greater expanded longitudinal flexibility, prevents apices of the stent portion from protruding into the graft portion and the blood vessel and reduces wear on the material forming the graft portion. The securing of the rail(s) relative to the graft portion according to the present invention eliminates the blood leakage that is typically seen with conventional stent-grafts that employ sutures. In this or any of the embodiments discussed herein, the ends of the graft portion may be secured to the stent portion by sutures.